Many container ships are equipped with separate cells to receive 40-foot containers and other cells to receive 20-foot containers. There is a tendency, however, to equip ships with 40-foot or longer cells only, in which, when necessary, 20-foot containers are then stowed end-to-end in pairs or larger numbers. In either case, containers are usually stacked on top of each other, these cells being sufficiently deep to hold a stack two or more containers high.
As is well-known, the so-called 20-foot standard container is actually 19'-101/2" long, while the 40-foot container measures 40 feet in length. Thus, when two 20-foot containers are placed in a 40-foot cell, there is a gap amounting to about 3" between the adjacent ends of the containers.
When two 20-foot containers are placed in a 40-foot cell, the outer ends of the containers (the ends facing away from each other) commonly fit between vertically extending pillars or beams which have an L-shaped cross section mating with the container corners, these corner beams being firmly connected to the structure of the vessel. However, the adjacent ends of the pair or pairs of containers are not supported in the lateral direction by any guiding surface connected to the ship. Thus, the pile of containers is relatively free to move in the cross direction as a result of the motion of the ship as it rides swells in the ocean.
To prevent this, the lowermost containers of the pile are placed on removable pins which engage holes in the corner pieces on the containers, or else the lowermost containers are placed between fixed cams and the mutual movement of the other containers in the same pile is prevented by providing loose double-sided piling pins or dowels between each upper container in the pile and the container beneath it. To maintain the horizontal position of the containers, these dowels must be placed at all four corners.
The job of placing the dowels and removing them during loading and unloading, respectively, of the containers requires the continuous or repeated presence of personnel in the hold and requires the handling of four relatively heavy objects for each container being loaded or unloaded. This work involves much climbing and is not without danger because it occurs from time-to-time that a dowel becomes stuck in the underside of the container and is hoisted with the container, only to fall out again at an inconvenient moment.
The foregoing discussion has primarily considered the situation which involves a cargo cell designed wide enough to receive only one cargo container. However, a further problem arises in cargo cells which are designed to receive two or more containers in side-by-side relationship, i.e., wherein the cargo cell is wider than the width needed to receive only one container. Normally, such containers are 8 feet in width and the cells are therefore dimensioned to receive either one container (or two or more end-to-end) with a few inches of lateral clearance, e.g., 8'2" wide, or else are designed to receive an array of containers side-by-side as well as end-to-end, in which case the cells are dimensioned to be a multiple of the container width plus some clearance.
It has been normal practice in the past to install pillars, special lashings or other attachments in the hold of a ship to receive these arrays of containers and to prevent lateral movement of the containers in the cell when the ship rolls or pitches, and to permit vertical stacking of arrays in a cell which has sufficient vertical depth to receive two or more stacked container arrays. Examples of such arrangements are shown in U.S. Pat. No. 3,583,350, Goldman, and British Pat. No. 1,188,316, Mitsubishi. The use of vertical pillars or beams, wire lashings, locking screws, dowel plates and other known arrangements all have serious disadvantages. In the case of pillars and support trusses, the structures must be relocated if the permutation of container lengths is changed. Others of the devices mentioned require that they be installed (or removed) at various stages during a loading (or unloading) operation, which is not only time consuming but also requires workers going into and out of the cargo cell repeatedly. Some of these structures also are not completely secure and can involve loss of cargo space, requiring that the cargo cell be initially designed longer or wider or both.